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Can Prefab Be Built On-Site?

Courtesy of Mark CocksedgeThis prototype prefab home in Hertfordshire, England, used an onsite digital manufacturing process.
This sounds like a contradiction in terms. But in fact a prefabricated house can be built on site when the factory is on site as well. Just such a house was built in the bucolic area of Hertfordshire, England. Industrial designer Bruce Bell of Facit Homes was looking for patrons to build the first prototype using his onsite digital manufacturing process. He was lucky to find property owners who not only sponsored this project but also became active participants in it.

The advantages to this type of construction were plentiful. The parts of the house could be built in a controlled environment and cut with precision CNC machinery (computer numerical control). These computer controlled machines can cut straight and curved pieces faster and more accurately than can be achieved with manually operated saws. With Facit's patented D-Process, they can transform a 3-D digital design into the actual house components.

The factory was set on the property close to where the house was to be built. The plywood components were digitally manufactured on-site, connected in place and then filled with cellulose insulation before it was set on the foundation.

The large multiple windows on the south side of the house encourage solar heating in the winter; the timber solar shades around the windows block some of the heat in the warmer months. These shades also cast a beautiful shadow on the house.

One of the owners, a very enthusiastic gardener, looked forward to restoring the garden on the property to its former glory after years of having been neglected. The house is slightly raised on screw piles, providing a much better view of the garden at the front and the back than was possible with the original house on the site. Several rooms have French windows facing onto the decking, and the large windows provide a great view of the plants, birds and animals.

Since moving in the owners have added a wildflower meadow with a spectacular array of flowers that have attracted a large number of beautiful butterflies.

Building with an on-site factory (or as they refer to it, a "mobile production facility" or MPF) in this manner saves the energy and time it would take transporting the components. It also creates minimal waste, protects the materials from the elements, and any errors that occur in the process can be quickly rectified. Using engineered spruce ply wood, the components are light to handle and lift into place avoiding the need for cranes or hoists.The end result is more predictable construction, built with quality control and with endless design possibilities.

In addition to building this house using this very efficient construction method, the house was also built to a very high level of energy efficiency. By positioning the house for optimal solar energy -- and including solar hot water and photovoltaic panels, 12 inches of insulation, and double- and triple-glazed energy-efficient windows -- the need for fossil fuel is kept to a minimum. Because this 2,153 square foot house is built to such high standards, it requires just a minimal heating system even in the coldest of winter days. And with net metering in England, the homeowners are paid back for the surplus electricity produced by their photovoltaic panels.

The MPF was later moved to another site in England and was used to build a recently completed 4,843 square feet house. Bell says that they have "pushed the process even further." They are producing the main structure or "chassis" on site, but are now producing additional elements for the construction -- such as the kitchen and staircase -- using their digital process, in the factory and transporting them to the site.